Cooling of wort – how to do it

When the boiling is complete, the wort must be cooled down to the temperature at which the yeast is to be added. Efficient and hygienic cooling makes the brewing more controlled and can improve the beer's aroma, clarity and shelf life.

At Lund Teknik, we swear by counterflow cooling ourselves. A counterflow chiller is efficient, relatively inexpensive, and can operate by means of gravity without the use of a pump. As the wort runs through a single, continuous stainless steel tube, the chiller is also significantly easier to clean on the inside than, for example, a plate chiller.

In our view, the counterflow chiller is quite simply one of the most ingenious solutions for cooling wort.

Why must the wort be chilled?

  • The continued bitterness from late hop additions is limited.
  • The hop aroma is better preserved.
  • The formation of DMS is reduced.
  • Proteins and polyphenols combine as a cold rub.
  • The risk of infection is reduced.
  • The wort cools down to the correct temperature for the yeast.

The goal is not necessarily to cool as quickly as possible at all costs, but to get the wort safely and controllably through the warm temperature range.

Hops, bitterness and aroma

As long as the wort is hot, the alpha acid in the hops continues to be converted into bittering compounds. The process slows down as the temperature drops, and the result depends, among other things, on temperature, time, hop quantity, alpha acid and the strength of the wort. In a planned hop stand, for example, the wort can be held at around 75–85 °C before it is cooled further. Rapid and controlled cooling after the late hop additions helps to preserve the volatile aromas.

DMS

DMS (dimethyl sulphide) can produce an aroma and flavour reminiscent of boiled sweetcorn or cabbage. The compound is formed from SMM, which can be found particularly in pale malts such as lager malt. A good, vigorous boil drives DMS off, but as long as the wort remains hot, new DMS can continue to be formed. Therefore, the wort should not be left hot for unnecessarily long after the boil.

Cold sweat and clarity

During chilling, proteins and polyphenols aggregate into larger particles that can precipitate. This is known as cold break or chill break. Good precipitation can result in clearer wort, less trub in the fermenter, and better physical stability in the finished beer. Chill haze occurs when proteins and polyphenols form small particles at low temperatures; it can disappear again when the beer warms up.

Oxygen before and after yeast pitch

It is important to distinguish between oxygenation of hot wort, oxygenation before adding yeast, and oxygenation after fermentation has started. Avoid unnecessary splashing of hot wort. When the wort has cooled to fermentation temperature, on the other hand, the yeast needs oxygen for healthy propagation, so the wort should be oxygenated immediately before the yeast is added. Once fermentation is underway, oxygen should be avoided because it can cause papery off-flavours and loss of fresh aroma.

Hygiene during cooling

All equipment that touches the wort after the boil must be thoroughly cleaned and sanitised. An immersion chiller can be placed in the kettle for the last 10–15 minutes of the boil. Hoses, valves and counterflow chillers must be cleaned immediately after use, before residues dry on.

Different cooling methods

Water bath

A water bath is cheap and simple and can be fine for small brews. On the other hand, the method is slow, often requires water replacement and makes it difficult to reach a low temperature. The pot must be kept closed to limit the risk of contamination.

spiral cooler

A stainless steel or copper immersion chiller is lowered directly into the wort while cold water runs through the coil. It is simple, visible and easy to clean, and the entire batch of wort is cooled at the same time. However, the cooling time depends on the temperature of the cooling water and the movement of the wort. Gentle stirring around the coil can improve the cooling.

Counterflow cooler – our preferred solution

In a counterflow chiller, the wort runs through an inner tube while the cooling water runs the opposite way around the tube. This provides efficient heat transfer and makes it possible to transfer the wort directly to the fermentation vessel at the desired temperature.

  • Effective and relatively reasonably priced.
  • Can run by pure gravity without a pump when the brew kettle is higher than the fermenter.
  • A continuous stainless steel pipe is easy to flush and clean on the inside.
  • The simple fluid path provides a lower risk of clogging than many narrow channels.
  • The temperature can be controlled by regulating the wort and cooling water flow.

For us, the decisive factors are precisely the combination of efficiency, simplicity, ease of cleaning, and the ability to run without a pump. The cooling water and wort must flow in opposite directions, and the chiller must be rinsed thoroughly immediately after use.

Plate cooler

A plate chiller can transfer heat efficiently, but the design presents significant challenges regarding both materials and cleaning. Many budget-friendly plate chillers are copper-brazed. This means that the wort comes into contact with the copper brazing, and copper can act as a catalyst for oxidation – especially when hot wort is simultaneously exposed to oxygen.

  • The narrow channels cannot be inspected visually.
  • Hops, proteins and trub can get stuck.
  • Most models cannot be taken apart.
  • Regular flushing is not always sufficient.
  • Copper brazing limits the choice and concentration of cleaning agents.
  • The radiator can look clean on the outside, even if there is still organic matter inside.

You can backwash and circulate cleaning fluid through a plate chiller, but it is difficult to check whether all channels are actually clean. Due to the combination of copper brazing, the risk of catalysed oxidation and the limited opportunities to inspect and clean the internal channels, we advise against using this type of plate chiller. We prefer a counterflow chiller with a continuous stainless steel tube instead.

Practical advice

  • Check the yeast's recommended temperature before cooling begins.
  • Measure the temperature with a clean and disinfected thermometer.
  • Position the boiler higher than the fermentation vessel if the counterflow chiller is to run by gravity.
  • Run cooling water and wort in opposite directions.
  • Adjust the flow until the outlet temperature is correct.
  • Recycle the hot cooling water for cleaning.
  • Do not add the yeast until the wort is at the correct temperature.
  • Aerate the cooled wort immediately before pitching the yeast – not later in the process.
  • Close the gate quickly after the transfer.
  • Rinse and clean cooler, hoses and valves immediately after use.

Our recommendation

There are several useful methods for cooling wort, but at Lund Teknik we prefer the counterflow chiller. It cools efficiently, can operate by gravity without a pump, is relatively inexpensive and – with a continuous stainless steel pipe – is far easier to clean and inspect than a copper-brazed plate chiller.

Happy cooling – and happy brewing!